Nonlinear optical (NLO) materials are unusual because their optical properties are affected by light. For instance, light polarizes certain materials. If the polarization is linear, then light radiated by the material has the same frequency as the absorbed light. NLO materials are polarized in a nonlinear manner. As a result, the frequency of the light produced by a nonlinear optical material is some value times the frequency of the light incident on the material.
Laser technology has benefited from the development of new NLO materials. However, known NLO materials often are suitable only for those applications for which they were particularly designed. As a result, new NLO materials continually must be developed having properties selected for a particular application.
Among known NLO crystals, borates of the type LiB3O5 and BaB2O4 are commercially important, at least in part, because they generate high-power laser light. LiB3O5 crystals have been used in patented devices. For example, Chuangtian et al.'s U.S. Pat. No. 4,863,283 describes an NLO device that uses a single LiB3O5 crystal. While LiB3O5 is widely used to convert near infrared light into visible light, it has an insufficient birefringence to allow direct second-harmonic generation of UV light. Thus, applications using LiB3O5 generally have been limited to selected wavelengths. In contrast, BaB2O4 exhibits a birefringence that is sufficient for UV generation, but its small angular acceptance limits general applicability.
The material CsLiB6O10 (Keszler, U.S. Pat. No. 5,684,813, incorporated herein by reference; Sasaki et al. U.S. Pat. No. 6,296,784) has an intermediate birefringence to that of LiB3O5 and BaB2O4, and is well suited for high-power UV generation. Unfortunately, CsLiB6O10 is an extremely hygroscopic material that is difficult to manufacture; as a result, it has achieved only limited commercial success.
Another borate crystal, Sr2Be2(BO3)2O (Chuangtian et al. U.S. Pat. No. 5,523,026), has been promoted for generating short-wavelength light. To date, crystals of this material have not been grown with sufficient size and purity to demonstrate commercial viability.
Recently, KBe2BO3F2 crystals have been used to generate wavelengths shorter than 200 nm [see Tagashi, et al. Optics Letters 2003, 28(4), 254-256]. However, KBe2BO3F2 has not been grown to commercially acceptable sizes, and it is too soft to be reliably cut and polished.
Doped and undoped materials known prior to the present application having the general formula (La,Ln)Sc3(BO3)4 (Ln=lanthanide) generally crystallize in the space groups Cc, C2/c, or C2. These latter groups commonly have been associated with the laser material Nd:LaSc3(BO3)4. See, Li, Yunkui; Aka, G.; Kahn-Harari, A.; Vivien, D.; Phase Transition, Growth, and Optical Properties of NdxLa1-xSc3(BO3)4 Crystals, J Mater. Res. 2001, 16, 38-44. Despite numerous studies reported in the technical and patent literature concerning Nd:LaSc3(BO3)4, apparently no one previously considered using these materials for nonlinear optical applications involving the production of UV and VUV light. The literature primarily addresses using Nd:LaSc3(BO3)4 as a laser material. Certain compounds belonging to the same series of materials also have appeared in the Russian-language literature. See, Kuz'micheva, G. M.; Rybakov, V. B.; Novikov, S. G.; Ageev, A. Yu; Kutovoi, S. A.; Kuz'min, O. V.; Zhurnal Neorganicheskoi Khimii; Disordered Structures of Rare Earth Scandoborates of the Huntite Family, 1999, 44(3), 352-366, incorporated herein by reference.
Known NLO compounds are limited in their application to generation of UV and VUV light, are damaged by exposure to high-power lasers, exhibit excessive absorption and light scattering of incident or absorbed light, and/or are too costly and time consuming for commercial production. As a result, there is a continuing need for new NLO compounds, methods for their manufacture, crystallization, and use.